Free trip circuit breaker



1953 R. c. INGWERSEN FREE TRIP CIRCUIT BREAKER Filed June 2, 1950 INVENTOR. RICHARD C- INGWERSEN Patented Jan. 13, 1953 UNITED STATES PATENT OFFICE FREE TRIP CIRCUIT BREAKER Application June 2, 1950,,Serial No..165,780

9 Claims.

This invention relates to electric circuit breakers which have overload protection and incorporate a thermal latch construction responsive to the temperature of the circuit current to break (or open) the circuit automatically upon the occurrence of a predetermined overload. More particularly, the invention relates to an electric circuit breaker of the same general construction and arrangement is disclosed in United States Patent No. 2,485,736, dated October 25, 1949, but modified to provide a trip-free action, by which the manual holding of the movable contacts against separation is not possible when a predetermined maximum current loading or value has been attained. In the prior construction it is oossible to override the overload protection by manually holding the contacts closed through pressure applied to the movable contact actuator button. An object of the present invention is to prevent such overriding action from occurring. .Another object of the invention is to provide an electric circuit breaker with which overriding of the overload. is possible for a predetermined lower current output, but is impossible for a predetermined higher or maximum current value.

The above and other objects and advantages residing in the construction, arrangement and combination of parts will be more fully understood and appreciated from a consideration of the following description with reference to the accompanying drawings and from the appended claims.

In the drawings:

Fig. I is a side elevational view of on practical form of the invention, with one-half of the casing structure removed, and showing the contacts and latch parts in closed position,

Fig. II is a similar view to Fig. I but showing the contacts and associated latch parts in open position,

Fig. III is a longitudinal section on the line A-A of Fig. I,

Fig, IV is a detail section on the line BB of Fig. I, and

Fig. V is a perspective view of the movable contact and latch unit in association with its supporting plunger actuator and guide structure.

Referring to the drawings, the casing structure of the circuit breaker is shown composed of two similar molded sections is and !2 of a suitable insulating material assembled together in opposed relation, with a dividing line indicated at the line It. Each casing section defines an internal cavity it which combine, as seen in Fig. III, to provide a-common cavity 18 in which the iii) fixed and movable contacts, indicated generally at 2% and 22, respectively, and the thermal latch mechanism, indicated generally at 2 3, are housed and the sides of which cavity it are movably closed by suitable cover plates (not shown).

The f red contacts 29 are carried upon conduotor terminals held embedded in recessed portions of the assembled casing sections l8 and [2 these sections being conveniently held together by transverse screw studs 23 and associated nuts 28 which may also serve to secure the said side plates in position to close the sides of the cavity E8.

The movable contacts 22 are carried at the outer ends of flexible arms 3b, which arms, at their inner ends, are secured upon inturned portions 32 (Fig. V) or" a U-shape thermal latch part 35 and or" an external temperature compensating finger assembly, indicated generally at at (Fig. III).

The U-shape latch part as is electrically connected in series with the movable contacts and their carrier arms 3 whereby this contact assembly is subjected to the electric current flow when the contacts are held closed, as seen in Fig. I. The compensating finger assembly 35, on the other hand, is electrically insulated from the circuit, as by the insulation 55, seen in Fig. III, whereby this assembly is not influenced by the temperature of the electrical circuit but only by the prevailing external temperatures, substantially as and. for the purpose disclosed in my copending application Serial No. 136,969 filed January 5, 1950, now U. S. Patent No. 2,587,162, granted February 26, 1952.

The thermal latch part and the compensator asse--... ly form a unitary assembly, which is guided for rectilinear sliding movement upon a combined fixed insulated guide structure and a plunger actuator 2 mounted within the structure iii.

The structure All comprises spaced apart block portions 44 which define an elongated slot 4'. between them in which a finger projection 48 on the actuator plunger 32 is guided for movement to actuate the thermal latch for resetting against spaced apart abutment ledges on the inner ends of the blocks A l, much in the same way as, and for the purpose disclosed, in the said prior Patent No. 2,485,736 in my name. In the present instance, however, the structure is such that the freely slidable upon the actuator 42 and, by the action of the springs 52, will immediately snap to the open contact position, as seen in Fig. II, when the thermal latch has (due to the heat generated in the latch by the current flow therethrough and the attainment of a predetermined maximum current overload) expanded sufiiciently outwards as to cause an inwardly directed lateral depression 54 in the latch 24 to leave the projection t8. When this happens the latch and movable contact unit is no longer held against the tension of the springs 52 but comes immediately under the control thereof to cause the contacts to open, as stated and as shown in Fig. II. In so moving, the latch 24 and the compensator finger assembly 56 slide past the opposite and respective blocks 84 of the fixed guide structure, which guides the thermal latch and movable contact unit for its required rectilinear motion into the contact open position; besides guiding the unit back to its reset and contact closed position when the actuator plunger 42 is actuated. Simultaneously with the opening movement of the said unit, the plunger actuator 52 is also moved to the outwardly projected position, as seen in Fig. II,

. when a collar portion (which may be colored red or, in some other distinctive color) is exposed and thus reveals to the eye that the circuit has been interrupted. This actuator movement results from the action of a spring 55 interposed between the casing and a T-shape block insertion 5t guidably mounted in a fork end portion of the actuator plunger, which fork end portion has the prongs thereof indicated at 53. The insertion 55 has its top portion 66 located opposite the inner ends of the arms 35 of the movable contacts and is constantly biased against the opposed end of the plunger actuator (actually against the base 62 of the fork) by the action of said spring 55, one end of which bears within a recess 53 in the divided casing parts ID, 12, whereas the opposite end bears within the recess 65 defined by the fork prongs 58.

It is to be noted that the latch part 3 1 is made from springy metal and that this part is initially formed so that it springs inwards at its outer end (as defined by the base of the U-shape latch part) so that upon this end of the latch part arriving at the abutment ledges 5!} it will immediately spring inwards into edgewise engagement with the ledges by the engagement of the edges of its end portions 34' with these ledges, which portions 34 lie upon opposite sides of the depression 5d, and which depression, it is to be noted, lies within the confines of the slot 45 and in the path of the finger projections is on the plunger 42.

It is also to be noted that the T-shape block insertion 56 is slidably mounted in the forked end portion of the plunger 42 and has its end portion 69 disposed on the side of the inner ends of the movable contact arms 3!) remote from the thermal latch part 34. It should also be borne in mind that, in the outwardly projected condition of the plunger 42 there is clearance between the finger projection 43 and the latch depression 54.

In operation, with the parts as seen in Fig. II, to set the circuit breaker for operation, it is merely necessary to push in the plunger e2 by applying inward pressure to the plunger button 68. This causes the finger projection 68 on the plunger to be brought into engagement with the outer edge of the base of the U-shape latch part 34 in the region of the inwardly directed edge presented by the depression 54. It will be appreciated that with the latch part 34 positioned in the contact-open position, as seen in Fig. II, the latch part is in an outwardly sprung condition, in which its outer end presses against the side surfaces of the blocks M so that the said end portions 34' are outwardly disposed with respect to the edges of the abutment ledges 53 an extent corresponding substantially to the thickness of the metal of the latch part 35. At the same time the outer edge of the finger projection 48 lies substantially flush with, or within, the outer edges of the abutment ledges 5!]. By providing the latch part with the inwardly directed depression 54 lying within the slot it is ensured (with the extent of the finger projection 38 as stated, and the latch part outwardly sprung, also as above stated) that the finger projection is able to engage the inwardly directed edge of the depression as the plunger 42 is pushed inwards. Accordingly, as the plunger is pushed inwards, the finger projection 48 will, by engagement with the inwardly directed edge presented by the depression 54, push the latch part 35 inwards, and with it, the entire unit constituted by the parts as. 56, 35, 22. At the same time, the springs 52 will be tensioned and the spring 55 will be compressed. Upon the outer edges of the end portions 34 of the latch part 365 arriving opposite the abutment ledges 55 they will immediately snap inwards into engagement with these ledges. The said unit will then be held in the contact closed position, as seen in Fig. I, in which position the circuit breaker is set for operation, with the springs 52 tensioned and the spring 55 compressed. During I the time that the plunger 62 is being pressed in to take up the clearance between the finger projection 58 and the latch depression 5d the end portion 69 of the plunger insertion 55 will be pushed away from the latch part a distance corresponding to the extent of this clearance with the important result that at the time when the latch part is positioned to engage the ledges 56 it will not be subjected to the pressure of the compressed plunger spring 55 and will be free to spring into engagement with the abutment ledges. Normally, upon the circuit breaker being thus set, the pressure applied to the plunger to push it inwards will be removed, so that the plunger is left free to be projected outwards by the action of its spring 55. Upon current being conducted through the thermal latch part 34, this part, being of bi-metallic construction, will be distorted and will distort outwardly at its outer end. The construction and arrangement, and the cali bration oi the thermal latch part 34, is such that upon the latch part being heated to an extent corresponding to a predetermined current value, the edge portions of the latch part defined by the latch portions 34' will leave the abutment ledges 50. When this happens (with the plunger 32 free as stated) the said unit will immediately and suddenly move outwards to the contact-open position, by the action of the springs 52. At the same time, the plunger 42 will move outwards by the action of its spring 55. The outward movement of said unit, into the contact open position, will be arrested when the unit arrives at the interior casing portions 51, which act as stops. Thus, in the normal operation of the circuit breaker the finger projection 48 will remain located adjacent the outer edge defined by the depression 54% and will be correctly positioned for engagement with said depression edge for re-setting the said unit.

It may happen, however, that pressure is ap plied to the plunger 42 to hold it in at the time when the edges of the thermal latch portions the latch depression 54.

the latch unit. can be re-set. .thatthedepression 54, travels inthe slot 4-5 and is plunger 42.

accuses the finger projection 48 will beheld in engagement with the inwardly directed edge defined by It is then necessary, therefore, that the latch part should be distorted further than the amount needed to enable the edges of the latch parts 34' to leave the abutment ledges 59 and that the amount of distortion should be suflicient to cause the trailing edge defined bythe depression Soto leave the finger projection 48. When this'happens, the said unit will be immediately freed to move to the contact-open position, by the action of the springs 52,:evenif pressure is still applied to-theplunger, which plunger is then no longer capable of actuation to prevent the said unit from moving automatically to the contact-open position. If, however,

the plunger continues to be held in at the time when the trailing edge of the depression 54 leaves the finger projection 48, the base of the U-shape latch part, in moving with the said unit to the contact-open position, will pass by the finger projection with the result that the finger projection43 will then become located adjacent the inside edge of the base of the latch part; that is the edge remote from-the depression 54. 'It is necessary, of course, that the finger projection 48 should be located adjacent the depression 54 in order that the plunger-can be actuated to reset the thermal latch unit in the contact closed position. It is also necessary that the plungen-efi. should be allowed to return to its re-setting position, by the action of its spring 55, in order that Bearing in mind always located in the path of the fingerproiection 48, if inward pressure is removed from the plunger 42 to allow it to return to its re-setting position (as seen in Fig. II) after the'latch. depression 54 has moved past the finger projection, due to the plunger being held in, as above statechthe finger projection, by engaging behind the depression, will automaticallydeflect the base of the U-shape latch part outwards from the side surfaces of the blocks 44, as the plunger is'restored to its re-setting position by the action of its spring 55, with the result that the plunger comes to rest with its finger projection 48' correctly located adjacent the latch depression 54.

It is to be noted that the T-part 55% is mounted on the plunger for movement therewith and that only the portion so thereof lies in the oath of the movable contact arms 39. However, this partfil'l .lies on the side of the arms as remote from the =ends'of the contact arms 39 will hold the plunger 42 in its pushed-in position, when the latch part is held enga ed with the abutment ledges 58', and the plunger is left free as above stated.

With the parts positioned as shown in Fig. I it is possible to release the said unit to move to the contact-open position byexerting a pull on the This will cause the sides of the plunger containing the fork prongs 58 to slide past the inside of the thermal latch part 3% and force the same outwards to release it from engagement with the abutment ledges 5D. This action is independent of the automatic circuit :breaker action and permits the circuit'breaker to be employed in' the manner of a manually actuable on and ofi switch.

- depression 54 has cleared the projection 48. At

the same time smaller current overload, such as falls within the range of the depression 54, is possible of being overridden by the operator holding the actuator button 68 depressed.

Having thus described my invention, what I regard as novel and Wish to cover by Letters Patent is:

1. In an electric circuit breaker having overload protection, casing structure, fixed contact means in said casing, movable contact means in said casing in opposed relation to said fixed'contact means, a thermal latch connected for movement with said movable contact means, said thermal latch being responsive to the heat of the electric current flow, abutment structure in said casing with which said thermal latch engages to hold the movable contact means in closed 1 relation to said fixed contact means, spring means operatively associated withsaid movable contact means, saidspring means being tensioned when the latch is engaged, and amanualactuator adapted';to-cooperate with said thermal latch" to set the latch in engagement with said abutment structure, means mounting said movable contact means and the associated thermal latch for movement as a unit relatively to said actuator in. the contact opening direction, due to distortion of thethermal latch upon the occurrence of a predetermined current overload, whereby to free the latch from said actuator and abutment structure and permit said movable contact means to be moved to open position by the tensioned spring means.

2. In an electric circuit breaker having overload protection, casing structure, fixed cont-act means in said casing, movable contact means in said casing in opposed relation to said fixed con- :tact means, a thermal latch connected for movement with said movable contact means, said thermal latch being responsive to the heat of the electric current flow, abutment structure in said 'casing with which said thermal latch is adapted to engage to hold the movable contact means in closed relation to said fixed contact means,-actuator means on said casing adapted to set the :thermal'latch in latched engagement with said abutment structure, means mounting said latch and movable contacts for movement as a unit relatively to said actuator upon the occurrence of a predetermined maximum overload, said actuator being incapable of actuation to hold the movable contacts closed against said maximum overload, said actuator being capable of actuation to hold the thermal latch and movable contact unit against such relative movement in overriding relationship to a lower current overcontact means in opposed relation to said fixed contact means, guide structure guiding said movable contact means for rectilinear movement toward and away from said fixed contact means,

spring means connected with said movable contact means to urge the movable contact means to open position, a thermal latch electrically connected with the said contact means and movable as a unit with said movable contact means, abutment structure adapted for engagement by the thermal latch to hold the latch in latched condition with the contacts closed, and actuator means for setting the latch in its latched condition, means mounting said latch and movable contact unit for free sliding movement with respect to said actuator means, said unit being free to move to open position upon the occurrence of a predetermined overload condition irrespective of the actuation of said actuator means.

4. In an electric circuit breaker with overload protection, fixed contact means, movable contact means in opposed relation to said fixed contact means, structure supporting said movable contact means for movement toward and away from said fixed contact means, said structure including a thermal latch carried for unified movement with said movable contact means, said latch being in electrical series connection with the contact means, abutment structure for said thermal latch to hold the latch in latched condition with the contact means closed, spring means for moving the movable contact means to open position when the latch is disengaged from the said abutment structure under thermal action, due to the occurrence of a predetermined overload condition, manual actuator means for setting said latch in the latched condition to hold the contacts closed, and means mounting said movable contacts and latch for sliding movement upon said actuator means'by said spring means, when the latch is disengaged, irrespective of the actuation of said actuator means.

5. In an electric circuit breaker having overload protection, casing structure, fixed contact means in said casing, movable contact means in said casing in opposed relation to said fixed contact means, a thermal latch in electric series connection with said movable contact means, said thermal latch and the movable contact means being of unitary construction, abutment structure in said casing with which said thermal latch is adapted to cooperate to hold the movable contact means in closed relation to said fixed contact means, actuator means on said casing adapted to set the thermal latch in latched engagement with said abutment structure and to close the movable contact means, means slidably mounting said latch and movable contact unit upon said actuator for unified movement thereon upon the occurrence of a predetermined maximum overload and means on said actuator and latch cooperable to hold the thermal latch against such relative movement in overriding relationship to a lower current overload.

6. In an electric circuit breaker having overload protection, casing structure, fixed contact means in said casing, movable contact means in said casing in opposed relation to said fixed contact means, a thermal latch connected for movement with said movable contact means as a unit, said thermal latch being responsive to the heat of the electric current flow, abutment structure in said casing with which said thermal latch is adapted to engage to hold the movable contact means in closed relation to said fixed contact means, actuator means on said casing adapted to set the thermal latch inlatched engagement with said abutment structure, meansmounting said movable contact means and thermal latch for unified sliding movement upon said actuator upon the occurrence of a predetermined current overload, and spring means for restoring the actuator means to initial position With respect to said movable contact and latch unit.

7. In an electric circuit breaker having over load protection, fixed contact means, said movable contact means being adapted to be mounted in opposed relation to fixed contact means, a thermal latch, structure supporting said movable contact means and latch to form a unit, said thermal latch being in electrical conductive relationship to said movable contact means, abutment structure with which said thermal latch engages to hold the movable contact means in position corresponding to closed contact position, actuator means guidingly mounted with re spect to said abutment structure, said actuator means being adapted to set the thermal latch in latched engagement with said abutment struc ture, means mounting said unit for free sliding movement upon said actuator in the direction corresponding to open contact position, and spring means constantly urging said unit in the contact opening direction.

8. In an electric circuit breaker having overload protection, insulated supporting structure, insulated plunger structure slidably mounted on said insulated supporting structure, said supporting structure providing abutment means, a unified thermal latch and contactstructure slidably mounted upon said plunger structure and guided for rectilinear movement with respect to the plunger structure, said latch being engageable with said abutment means, means on said plunger structure engageable with said latch by movement of the plungerstructure in one direction only to set the latch in engagement with said abutment means, spring means constantly urging the said latch and contact structure into open position, and spring means for restoring thte Iplunger to initial position for resetting the la 0 9. An electric circuit breaker as claimed in claim 9, said latch having a protruding ledge portion for location against said means on the plunger structure, said plunger structure being capable of being manually held to override disengagement of the latch from the said abutment means until the latch ledge portion has cleared said means on the plunger, when the plunger structure is no longer capable of holding the latch against disengagement from said abutment means.

RICHARD C. INGWERSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,492,967 Donle May 6, 1924 2,210,261 Sachs Aug. 6, 1940 2,217,488 Mahnke Oct. 8, 1940 2,485,736 Ingwersen Oct. 25, 1949 FOREIGN PATENTS Number Country Date 560,004 Great Britain Mar. 15, 1944 614,510 Great Britain Dec. 16, 1948 781,446 France Feb. 25, 1935 

